A ferritic stainless steel is used for a can body for hot-water in an electric water heater or the like because the ferritic stainless steel has no risk of stress corrosion cracking. This can body is typically assembled by tungsten inert gas welding (TIG welding). In TIG welding, the formation of an oxide film, referred to as a temper color, on the surface of the stainless steel sometimes deteriorate the corrosion resistance. Moreover, the generation of a Cr depletion region which is caused by the invasion of nitrogen in a weld bead sometimes deteriorate the corrosion resistance (this phenomenon is referred to as sensitization). Therefore, to reduce the formation of the temper color or the sensitization during welding procedure, it is recommended to perform gas shielding using Ar gas over both face and back surfaces of the welded portion.
However, in recent years, an increase in complication of the can body structure increases the welded portion where the gas shielding cannot be sufficiently performed.
In the application of the steel exposed to a severe corrosion environment, for example, the inner surface of a can body for hot-water in an electric water heater, a temper color formed in a welded portion owing to insufficient gas shielding is generally removed by a posttreatment such as an acid treatment and an electrolytic treatment.
However, the more frequent use of a stainless steel which is more excellent in the corrosion resistance than that of the conventional stainless steel for the can body increases the load of the posttreatment. In particular, it is difficult to remove the temper color generated in a weld heat-affected zone. Thus, it is required to improve the removal performance for the temper color in order to reduce the load of the posttreatment.
Patent Literature 1 discloses the technique that stabilizes C and N, which causes the sensitization, by adding Ti and Nb in order to prevent the sensitization of the welded portion.
Patent Literature 2 discloses the technique that uses the component composition satisfying Cr (mass %)+3.3Mo (mass %)≧22.0 and 4Al (mass %)+Ti (mass %) 0.32 in order to improve the corrosion resistance of the welded portion. Patent Literature 3 discloses the technique where a large amount of Cr is contained or Ni and Cu are contained in addition to Cr in order to improve the corrosion resistance of the welded portion on the side of a penetration bead which is formed by TIG welding without back gas shielding.